In response to the energy saving of automobiles, etc., there is a need for an electromagnetic component to be used in the automobile, etc., in which a magnetic circuit can be controlled more precisely, and energy saving and an improvement in magnetic response speed can be achieved. Accordingly, a steel material to be used as a raw material of the electromagnetic component is required, as magnetic properties, to be easily magnetized by a low external magnetic field and to have small coercive force.
Accordingly, a soft magnetic steel material, the magnetic flux density within which is likely to response to an external magnetic field and which is inexpensive as compared to Ni, Co, or the like, is usually used. Specifically, extremely low carbon steel (pure iron-based soft magnetic material), etc., including, for example, no more than approximately 0.1% by mass C, is used as the soft magnetic steel material. The electromagnetic component (hereinafter, sometimes referred to as a soft magnetic steel component) is typically obtained in the following way: this steel material is subjected to hot rolling, and then to pickling, a lubricating treatment, and wire drawing processing, etc., the last three steps being referred to as secondary processing steps; and a steel wire obtained by the above steps is sequentially subjected to part molding and magnetic annealing, etc.
The aforementioned electromagnetic component is required to have corrosion resistance depending on a usage environment. Electromagnetic stainless steel is used for the part required to have this corrosion resistance. Electromagnetic stainless steel is special steel that combines magnetic properties and corrosion resistance, and applications thereof include: parts utilizing a magnetic circuit in which eddy current suppression is indispensable, such as an injector, sensor, actuator, and motor; electromagnetic components to be used in a corrosive environment; and the like. As the aforementioned electromagnetic stainless steel, 13Cr electromagnetic stainless steel has been used conventionally and often, and for example, Patent Document 1 presents a technique for improving the cold forge ability and the machinability of the 13Cr electromagnetic stainless steel. However, it is more difficult to machine the 13Cr electromagnetic stainless steel than extremely low carbon steel that is more excellent in cold forgeability, and the material price thereof is high because of high contents of an alloy element, which causes the problem that, when an alloy price is steeply increased, the material price is increased in tandem therewith or it becomes difficult to purchase the material. Additionally, for the electromagnetic stainless steel, for example, used in fuel cell vehicles, etc., the improvement in corrosion resistance is recently demanded.
On the other hand, the techniques disclosed, for example, in Patent Documents 2 and 3 are presented as extremely low carbon steel. These techniques are made mainly for the purpose that the strength and the machinability are improved without deteriorating the magnetic properties by controlling steel material components and the dispersion state of sulfide in the steel, and are not studied for the case where corrosion resistance is required.
From the above description, there is a need for an inexpensive steel material having excellent magnetic properties and also having greater corrosion resistance than the aforementioned electromagnetic stainless steel.